Manual vs automatic What is desirable for MPG?

[Blacktree]

Originally Posted by Joggernot

I have a 2018 Honda CRV with CVT. I shift to neutral and coast whenever possible.

My previous daily driver was a Jetta TDI with a 5-speed manual gearbox. I found that trying to invoke DFCO was a waste of time. But coasting in neutral had very good results. Part of that was because of the diesel engine; they can run super-lean at idle. And I could coast a lot further in neutral than I could in gear.

[Piotrsko]

Since 2000 diesels have been generally no fuel on coast,or a least for Cali. Both the F250 & Golf. It returns fuel when it drops below idle rpm, gets Really prissy if it is still in gear And the f250 can command full fuel to override the brakes or any other drag. Other than compression drag, I can't see the point unless you are in stop&go traffic

[cRiPpLe_rOoStEr]

Originally Posted by Blacktree

My previous daily driver was a Jetta TDI with a 5-speed manual gearbox. I found that trying to invoke DFCO was a waste of time. But coasting in neutral had very good results. Part of that was because of the diesel engine; they can run super-lean at idle. And I could coast a lot further in neutral than I could in gear.

When my maternal grandfather had a Brazilian S10 with the mechanically-governed MWM turbodiesel engine, he did neutral-coasting whenever possible with good results. It's been often pointed out as a rule-of-thumb that engines with EFI, including Diesels, wouldn't respond so well to it. DFCO is often pointed out as safer because of shorter braking distances anyway.

[MetroMPG]

Originally Posted by User1

I thought for sure I'd find a pretty good post on manual vs automatic tranies somewhere here! If there's something I missed, please let me know.

Here's a thread I started about how the EPA testing procedure handicaps manual transmissions:

>> Shift points: EPA testing of manual transmissions (why beating MT ratings is easier)

I am persuaded if someone can convince me that my next car should be an automatic. I tend to go for smaller and less powerful vehicles...

I've done a head-to-head comparison (city & hwy) of a 4-speed AT against a 5-speed AT with Nissan's 1.6L motor (in the Canadian Micra platform, which was the same as the previous generation U.S. Versa platform).


Despite the cars having essentially the same MPG rating, the manual gets significantly better real-world fuel economy. The only "special" technique used in the manual car was shifting to the highest usable gear after accelerating. No drafting, no coasting in neutral, no engine-off.

>> Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L

The above results are mirrored in the "real world" by multiple owners:

After nearly 387,000 km tracked in our fuel log by 43 Micra owners over 995 fill-ups, the manual transmission cars are using 12% less fuel than the automatics.

>> https://micra-forum.com/mgarage-stats.php


As has been said above, the older automatics will suffer more by comparison than the modern ones. A CVT or dual clutch automated manual will close the gap, but I still say the manual is still the better choice in the hands of a non-brain-dead driver, regardless of the EPA ratings.

The exception may be for drivers who do 100% highway driving. Some of the newer CVT's may win out there. But who does that??

I'll dig up the Mitsu Mirage stats for comparison (uses a CVT automatic).

[Isaac Zachary]

My 2 pennies:

• CVT is possibly the best, at least in theory. But many gears may make it too close to tell.
• For a manual and automatic to be comparable, the manual needs one more gear since it doesn't have a torque converter that multiplies torque acting as a lower 1st gear when taking off from a stop. But today it's far more prevalent to see manuals with fewer gears than automatics. Anyone else want an 11 speed manual in their minivan? (I do).
• Computers have come a long way, but a very knowledgeable and conscientious driver with a manual should be able to match or even possibly exceed the efficiency of a modern day automatic. This is because an automatic tries to be as economical as possible yet give the drive the performance it think he's looking for. Sadly, the best engine efficiencies tend to be right at the point automatics start downshifting thinking you want more power when all you want to do is slowly accelerate with about 90% throttle and low RPMs, hence why you may be able to beat an automatic with a manual.

[freebeard]

My next vehicle should have single-speed twin motors.

[aerohead]

Originally Posted by User1

Hello all,

I thought for sure I'd find a pretty good post on manual vs automatic tranies somewhere here! If there's something I missed, please let me know.

OK just to let you know, I'm a manual fan here. I am persuaded if someone can convince me that my next car should be an automatic. I tend to go for smaller and less powerful vehicles, I don't need the biggest or greatest. I always go for used vehicles too. The big thing here is that we have a good idea the trans that most desirable for MPG.

The market trend is towards automatics.
1) Theoretically, a CVT is the ideal, as far as keeping the engine in it's BSFC 'sweet-spot' during transient loading.
2) A 12-speed trans equals the efficiency of a CVT.
3) Automatic transmission vehicles cost less to manufacture than manuals. They are preferred by bean-counters.
4) Automakers can better achieve EPA Mobile Sources Emission Standards with automatic transmissions, as they can completely control shift points for the lowest emissions/ highest mpg.
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In highway-only, long-range cruising, there's zero advantage with a manual any more.
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In urban traffic one will come to despise a manual transmission (when PORSCHE began to offer automatics, that was the writing on the wall ).
Try eight-hours of stop-and-go, between Paso Robles and Anaheim sometime.
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What you're looking for is to, get the engine at it's lowest BSFC and keep it there. Automatic CVTs and 10-speeds can do that better than ever before. And in an 'emergency', you don't have to figure out what gear your in, and which gear to go to.

[Piotrsko]

Did the paso to Anaheim. Try Lancaster to san diego via 395 or anything through the 5 level @ noon or after. Makes for a beefy clutch leg if you only have 4 gears not better even with 12

[Isaac Zachary]

One advantage of the CVT no one has mentioned yet is it can keep the engine from constantly accelerating and decelerating. When shifting, you're losing small amounts of kinetic energy everytime the engine decelerates.

I think the type of manual transmission would make the difference. Something with automatic-like clutchless shifting would be nice. Paddle shifting with a well designed dogbox would make city driving more tolerable.

I think it's not just the amount of gears but the amount of acceleration you'll be doing that can make driving a manual unbearable. If you make it from 0 to 60mph in 3 seconds but need to shift between 12 gears to get there, that would be quite horrible. But if it takes 3 minutes, not so much.

[mort]

Originally Posted by Isaac Zachary

Sadly, the best engine efficiencies tend to be right at the point automatics start downshifting thinking you want more power when all you want to do is slowly accelerate with about 90% throttle and low RPMs, hence why you may be able to beat an automatic with a manual.[/list]

My 20 year old Volvo with only 4 gears in the automatic has a shifter position that allows the driver to hold any gear and up or down shift whenever they please. I'm sure most modern automatics have that feature, often as paddles.
-mort